In conventional microcircuits, large numbers of electrons flow and their collective action can be characterised in terms of conventional current. However, in quantum microcircuits, the dimensions of circuit component parts are constructed to be sufficiently small that the flow of individual electrons is controlled and the behaviour of the electrons needs to be described in terms of their quantum mechanical wavefunctions.
With such very small circuits, problems arise in providing external connections for control signals that are used to perform logical switching.